1. Field of Invention
This invention relates to the measurement of liquid flow, particularly to metering fluid intake for proper human hydration.
2. Prior-Art--Hydration Systems
Physicians generally agree that for optimum health and proper nutrition, each person should drink at least eight 240 ml (8-oz) glasses of water a day under normal conditions. This is because fluids are continually lost from the body at varying rates throughout the day, the rate of loss increasing during exertion. Serious consequences result if this water is not replaced in the proper amount and at the proper time. These consequences include fatigue, nausea, loss of consciousness, and, potentially, death. This problem is compounded because thirst is not a reliable indicator of the need for hydration (water); one can be in severe need of hydration, yet not feel thirsty.
In all athletic endeavors, it is vital to maintain a proper level of hydration in one's body. It is well-known that proper body hydration is essential before, during, and after strenuous exercise. See, for example, "Exercise and Fluid Replacement", V. A. Convertino, et al., Medicine and Science in Sports and Exercise, Vol. 28, No. 1, pages i-vii, 1996. While ad libitum fluid ingestion is useful, and even required, it does not generally provide sufficient hydration.
A survey of 3,003 Americans, released on May 11, 1998 by the Nutrition Information Center at The New York Hospital-Cornell Medical Center and the International Bottled Water Association, found that most Americans are probably only getting about a third of the valuable hydration benefits they need." says Barbara Levin, R. D., Ph.D., director of the Center. "The vast majority aren't drinking enough water to begin with, and, to make matters worse, many don't realize that beverages containing alcohol and caffeine actually rob the body of water."
In hospitals it is frequently vital to maintain the rate of hydration of a patient. In some cases the rate of hydration is partially known by the rate of delivery of intravenously supplied fluids. According to the study, "Intravenous vs. Oral Rehydration: Effects on Subsequent Exercise-Heat Stress", J. Appl. Physiol. 82(3): 799-806, 1997, research suggests that after exercise-induced dehydration, intravenous and oral deliveries were equally effective as rehydration treatments. However, intravenous delivery of fluids is invasive and subject to complications. Intravenous delivery is also not a practical means for preventative hydration. In the past, the patient's total oral consumption of fluid has been monitored and maintained by guesswork. Patient care is often deficient, however, because there is no accurate measure of the patient's rate or quantity of hydration. This results in patient upsets and increases time and effort required by the medical staff.
According to the March, 1994 issue of the Canadian Medical Journal, studies have shown that an increase in water intake can actually reduce fat deposits. Drinking enough water is the best treatment for water retention. Since water is the key to fat metabolism, it follows that the overweight person needs to drink more water. Although, as stated, on the average, a person should drink eight eight-ounce glasses every day, the overweight person needs one additional glass for every 25 pounds of excess weight.
According to the Journal of the American Dietetic Association, Vol. 99, No. 2, February, 1999, in the article titled: "Water: An Essential but Overlooked Nutrient", "New research indicates that fluid consumption in general and water consumption in particular can have an effect on the risk of urinary stone disease; cancers of the breast, colon, and urinary tract; childhood and adolescent obesity; mitral valve prolapse; salivary gland function; and overall health in the elderly. Dietitians should be encouraged to promote and monitor fluid and water intake among all of their clients and patients through education and to help them design a fluid intake plan."
Various liquid containers for supplying drinking water are commercially available. They range from a simple bottle to a sports-oriented backpack reservoir with a delivery tube. Several models of a backpack reservoir system are sold by FasTrak Systems, Inc., P O Box 1029, Weatherford, Tex. 76086-1029, under the mark CamelBak. The HydroBak.TM. model comprises an insulated fluid reservoir which holds 1.5 liters (50 oz). After filling, the reservoir is placed in a sack-like container. A pair of straps holds the sack against the user's back. In an alternative design, the reservoir is strapped to a waist-pack on the user's waist in a similar fashion. A flexible tube, of length approximately 38 cm (15 in), and diameter of approximately 0.95 cm (3/8 in) connects to the reservoir. A valve-mouthpiece is secured to the distal end of the tube. Some prior-art valves are opened by a biting action; others are opened by forcing the valve open with the user's mouth parts. To obtain water (or another fluid) from the reservoir, the user simply opens the valve and creates a suction with her or his mouth. In response to this suction, fluid leaves the reservoir and is delivered to the user's mouth for swallowing. This system provides ad-libitum hydration only. It does not accurately indicate the volume of fluid consumed, or the rate at which the fluid has been consumed. Nor does it provide a reminder for users who may be dehydrated but not thirsty.
A similar sport hydration system is taught by Boxer et al. in U.S. Pat. No. 4,526,298 (1985). In this system, the user wears a back-mounted, liquid-filled reservoir. A flexible tube, similar to the above, connects the reservoir to a hand-held, hand-operated pump. When the pump handle is squeezed, the pump delivers either a stream or a spray of water, depending upon the adjustment of a nozzle attached to the pump's output orifice. The user can thus spray a stream of liquid into her or his mouth to be swallowed, or optionally douse her or his face or other body areas with a cooling mist.
Operation of Boxer's pump handle requires the user to have one band free. This is not always possible when the user is riding a bicycle, climbing a mountain, or skiing. More importantly, although the spray produces a feeling of comfort, it does not contribute to the user's level of hydration. Further, Boxer's system does not measure the volume of fluid delivered over a predetermined period of time. While dousing one's body with a cooling mist may feel good, it does nothing to maintain proper hydration.
A liquid dispenser meter is taught by Griffiths et al., in U.S. Pat. No. 4,350,265 (1982). This meter is mounted on a bottle which contains an alcoholic beverage. To dispense the alcohol, the bottle is inverted, causing the alcohol to fill a measuring chamber. Pressing on a plunger causes (a) a predetermined volume of liquid in the chamber to be dispensed, and (b) a counter to be advanced by one count. Thus by knowing the volume dispensed each time the plunger is pushed, and the volume of liquid in the measuring chamber, the total volume of liquid dispensed through the meter is known. While it provides information about liquid volume dispensed, this system does not display the volume dispensed as a function of time. Further, the bottle must be inverted in order to dispense liquid, the flow being urged by gravity. A user such as a bicyclist would not use this system because it dispenses an alcoholic beverage, which, as stated, actually decreases hydration. Also the bicyclist cannot conveniently get water from the inverted bottle and cannot use oral suction to dispense liquid from the bottle. The rate of consumption is not indicated and there is nothing to remind the user to drink. Thus, even if this system could be used by inverting the bottle, Griffiths' system provides only ad-libitum consumption of liquids and cannot ensure that the user maintains proper hydration.
Sigdell et al., in U.S. Pat. No. 3,919,455 (1975) teach an apparatus which measures the volume and flow rate of liquids. This system uses a siphon-suction principle in which a container is filled by suction, then when a predetermined level is reached, a siphon causes the container to drain. Electrical sensors detect the evacuation of the container and signal that the container is ready for another fill-and-drain cycle. While this system provides information about liquid volume dispensed, it does not display the volume dispensed as a function of time. Further, suction is used only to fill the chamber. If the siphon action is not allowed, the chamber will not drain and the chamber will remain full. Even if repeated siphon and suction cycles were employed, this system would not be practical in human hydration applications. The entire contents of the container are drained in each siphon cycle. Thus, the user would be required to swallow the entire volume of the container. Because of the container's fixed size, it would not be possible for the user to withdraw a single sip of liquid at one time, and at a later time withdraw a mouth-full from the same container. Because of these limitations, this system is not applicable to maintenance of hydration.
None of the prior-art fluid supply systems accurately reports the rate of fluid consumption. Further, none of the prior-art fluid supply systems indicates, in advance of the user's thirst, that it is time to consume more fluid. By the time a user is thirsty, she or he is already partially dehydrated.
3. Prior-Art--Flow Meters
Many prior-art liquid flow meters are known. In general, they comprise the following types: differential pressure, positive displacement, velocity, and mass meters. In differential pressure meters, flow is inferred from the pressure differential which arises from flow in a predetermined geometry. These include orifice, Pitot, venturi, and other well-known types. In positive displacement meters, flow is related to the movement of a member within the meter. These include rotary vane, gear, and piston types, among others. Velocity types measure the velocity of the liquid through a region of known cross-section. These include turbine, sonic, and ultrasonic types, among others. Mass flow types measure the actual passage of mass through the meter. These include thermal, optical, coriolis, and other types.
U.S. Pat. No. 4,489,616 (1984) to Priddy teaches a "Digital Fluid Flow Meter". In this meter, fluid impinges on the vanes of a rotary impeller, forcing it to turn. FIG. 1 shows the principal elements of this meter. Liquid enters the meter through external connection 32. It flows through channel 34 and exits into the chamber bounded by circular opening 18. The fluid flow impinges on radial vanes 26 of impeller assembly 20, which is free to rotate on bearings (not shown). Fluid fills the spaces 28 between vanes 26. Fluid leaves the region surrounding the impeller through an outflow channel (not shown) along flow lines 54. The fluid finally exits the flow meter through orifice 50 and exit fitting 52. The rate of rotation of impeller 20 is proportional to the rate of flow of the fluid passing through the meter. The driving force for fluid motion is generally derived from elevated pressure applied to the fluid entering at connection 32.
A magnet 60 is secured in one of the vanes 26 of impeller 20. An external coil is placed in the vicinity of the impeller. As the impeller turns, the motion of the magnet induces a voltage in the coil. This voltage creates a current generally in the form of transient pulses which have a rising edge as the magnet approaches the coil, and a falling edge as the magnet retreats. These pulses are counted using conventional digital electronic circuitry. The pulse rate frequency is equal to the rate of rotation of impeller 20, and thus is directly proportional to the rate of flow of liquid through the meter assembly. With appropriately tight tolerances, Priddy's meter can be made to approximate a positive displacement flow meter.
While Priddy can accurately measure flow volume and rate, his system does not solve the aforementioned hydration problems.